Assuefaction
by Stripes that Parallel
Summary: With change comes new habits. In the blood-soaked arenas of Infinity, Fai fights an inner battle for self control. It is hard enough trying to face the crimson eyes that follow him, but harder still to face the threat that lurks beneath his own skin.


**Assuefaction**

[With change comes new habits. In the blood-soaked arenas of Infinity, Fai fights an inner battle for self control. It is hard enough trying to face the crimson eyes that follow him, but harder still to face the threat that lurks beneath his own skin.]

**Rating - T **[lots of blood and Kuro's potty mouth]

**Warning** \- Buckets of angst, psychological unsteadiness, violence, blood-drinking, sad and angry boyfriends, semi-abrupt ending, possible tense-changes, and a few grammar edits needed I'm sure.

**Disclaimer** \- I don't own anything, clearly, except a poopy HP and a currently dysfunctional MSW, which is why I had to write this mostly in plain text docs and cry over nonexistent formatting. Enjoy!

* * *

_Assuefaction - (n.)_ The act of accustoming, or the state of being accustomed; habituation.

* * *

The sunrise came abruptly, announced through a nauseating wave of sherbet-pink that spilled across the smog-laden gray of Infinity's skyline and ripped through the too-thin curtains hung over the solitary window in the bedroom.

Fai felt the heat on his sleep-deprived skin, tasted the cool musk that crept through the cracks of the poorly-insulated window frame every morning, and scowled. It was much too early, his muscles aching with the regaining of consciousness and the vague memory of a grueling "Chess" match from the day before, and he would give anything to just keep his thoughts from awakening for _five more minutes_ -

Sharp rapping against the open bedroom door drilled painfully into his ears, and he twitched despite himself as Kurogane's gravelly voice broke the stillness of the room.

"Get up. We've got another match today."

The implication of an early wake-up call was not a light one; the ninja's clipped tone spoke of a long day of preparation for the group, both mental and physical.

Silent, Fai stared the crook of his arm. He could feel Kurogane's eyes trained on his back, burning into his skin in their search for acknowledgement. When none was given, Kurogane huffed low in his throat, turned from the doorway, and disappeared down the hall.

For only a moment more, Fai stayed in bed, squeezing his eye shut against the ghosting presence that he still felt in the doorway, demanding to be seen, demanding for _anything_.

A curl of warmth, thirsting and predatory, swelled in his chest.

Disgusted, he tossed the comforter off and stood from his bed, squinting in the swath of too-bright pastels that fell across him.

_It's just another day_, he told himself firmly, and proceeded to get dressed.

* * *

Each meal was an adjustment. Bread had little more flavor than sawdust; milk was a near-tasteless blend of water and calcium; meat was an overwhelming surge of heat and pulse and _prey_.

Gradually, he had learned which foods to stay away from, and which ones were tolerable enough to resist spitting back out. He had fallen into a routine of sorts: tea for breakfast, vegetables for lunch, and a piece of bread with whatever dinner he or Sakura had managed to produce.

At lunch, he ate his usual mix of greens; "Rabbit food", Kurogane had _tsk_ed at him. Idly, Fai had wondered if this was what animals tasted. Was everything but their desired meal a mix of flavorless chemical compounds eaten as a last resort?

His stomach had twisted uncomfortably then, a single eye darting uneasily across the table into the steady gaze that had been studying him ever since his fork stilled in his thin fingers, because how, _how_ could he associate Kurogane to nothing more than a meal?

_That's what he is_, a voice, venomous and sharp, murmured to him, _he is _yours_ and _yours_ alone_.

Fai scraped off his half-eaten plate with a tense breath, placed it with a clatter into the sink, and left the room without a word.

* * *

"They have to have some connection to them," Syaoran thought aloud from the one side of the prep room, his brow furrowing. "I mean, why else would we be pinned up against them so soon? Eagle has to have some reason for it, right?"

Kurogane scowled, flicking out a role of bandage tape.

"Whatever the bastard's doin', it doesn't make sense to me," he growled lowly, wrapping the tape with a few quick tugs around his forearm, "He knows the hime's injured. He's pushing her on purpose."

Syaoran frowned thoughtfully, pulling his hands through his open-knuckled gloves.

"Do you think he's trying to test all of us?" he asked after a moment, flexing his fingers. "It makes sense. We've lasted this long...maybe he wants to see how far he can push our limits."

Crimson eyes flickered over to the blond on the opposite bench.

"If that's what he's aiming at," Kurogane muttered, his eyes narrowing, "he better be ready for one hell of a ride."

A shrill beep sounded over the intercom in the room, drawing Syaoran's eyes up to the yellow-hued ceiling. He swallowed, clenching his fists.

"This is the last one for this week," he said quietly, his dark gaze determined. "One more."

Fai stood calmly, a single pale eye watching absently as the metal gate at the front of the room drew up with a thunderous rumble, opening to the wild roar of the arena.

"One more," he echoed quietly.

* * *

There was blood. There was so much blood: caked into their clothes, painted into their palms, stained on the hilts of their weapons. The crowd was deafening, screeching viciously, beating on their stands and waving their diamond-patterned flags. But there was so much blood, and it was so loud, and all Fai could smell was a vile mixture of iron and salt and sweat and heat and -

_Fai-san._

Panting hoarsely, he jerked the razor-edged front of his whipblade from his downfallen opponent, snapping the weapon into place as he turned to face their resolute leader. Sakura stared down at him firmly from her perch, her thin brows drawn together in concentration. He nodded his head curtly, turning back to the battle at hand and blinking the sweat from his eyelashes.

He knew he wasn't as focused as he should be. If Syaoran's theory was right, Eagle was testing them. This match was about leaving an impression; their opponents had been chosen strategically, and defeating them - defeating them _well_ \- was the test. Anyone could kill if a weapon was placed in their hands; _how_ the kill was performed was what the mafia was observing.

It was despicable, lewd, and cruel, and Fai hated every moment of it. But even so, despite the flood of scents and auras and too many things for him to process at once, and the aching protest of his sore muscles, he knew he had to keep fighting. Just for one more match.

"One more," he murmured breathlessly, and whipping his weapon open again with a deadly _shhnik_, he dove back into battle.

Syaoran, one eye blooded and shut, was fighting with everything he was worth, roaring with the exertion of it as he slashed his twinswords at the thighs of his opponent, knocking them to their knees. Fai could see the exhaustion growing in the boy with each adrenaline-fueled move. Kurogane was tiring too. The ninja, gaze locked on his opponent and teeth bared, pulled Souhi into a deadly dance of master and weapon, sweat beaded on his dark brow.

Fai was halfway to aiding them when a sudden, searing tug pulled at his chest, and for one breathless moment he thought he had been wounded. There was a pulse thudding inside his veins, erratic and flowing, but it wasn't _his_ \- and abruptly he found himself staring at Kurogane, doubled over with a tanned hand digging into his side, hissing sharply through gritted teeth. Syaoran gave a sudden shout, and Sakura's mental connection could be felt drawing taunt in Fai's mind, and for one horrifying second all he could hear was Kurogane's pulse thudding in his ears.

Then he _felt_ it; hot iron flooded his senses, and he could taste it on his tongue, crackling across the roof of his mouth in a surge.

An untameable, hellish rage brewed up inside him, and before he could process it, he had moved in a blur, his whipblade ringing across the checkerboard floor. He couldn't think, he couldn't even recognize his own movements, but he could feel his limbs straining with unbridled strength, his muscles rippling with actions he had not told them to do - and all could think was an outraged jumble of _How dare they touch him_.

No one would hurt him. _No one_.

And then, the arena was quiet. He stared forward dumbly, blinking as if coming out of a dream. He could see the mouths of the audience moving, feel the vibrations of their chants beneath his feet, but he couldn't hear them; all he could hear was the thudding of his own heartbeat and the uneven, throbbing pulse of the shallow-breathing warrior behind him.

The noise erupted without warning into full force. The shrill whistle of the referee and a thunderous yell of, "Penalty! Black Team - illegal use of weaponry!" mixed in with the roar of the crowd; from the center box, a white-garbed man dismissed the charge with a flick of his hand. The referee hesitated, and then blew the whistle again, waving a black flag.

But Fai couldn't register any of it, not the win, or the cheering, or the rumbling murmur of question behind him; he stood staring, transfixed, at the sight of two claw-mangled men, crumpled and bloody at his feet.

* * *

"What the _hell_ got into you back there?"

Fai stared off at the back wall of the infirmary, his lips drawn into a tense line. The moment Kurogane's grip had latched onto his arm - firm enough to bruise against his skin and alarmingly threatening - he had lashed out with protests, and the ninja practically had to drag him off the arena. Now he was cornered, that heated gaze uncomfortably steady and his own joints uncomfortably tight.

"You're hurt," Fai murmured dismissively. Kurogane growled low in his throat, stepping closer.

"Would you forget about the damn wound," the warrior snapped, "I'm fine. Doesn't matter. I need to know what the hell just happened." His breath shuddered slightly, his brow twisting. "I need to know _why_."

Silent, Fai glanced at the floor.

"Mage," Kurogane breathed out, his voice gravelly with desperation, "Don't give me this shit right now. You barely kill to begin with, but you have _never_ killed like that."

Fai's brows furrowed, his downcast gaze narrowing. He whispered slowly, his voice quiet, "They could have killed you."

The ninja scoffed, pressing his palm a little tighter against his side before pulling it away.

"Like hell they could've," he grumbled, and at the uneasy sheen that emerged in the blond's gaze, he moved away to rummage through a medicinal cabinet. He rattled through different metal drawers noisily before grabbing a roll of gauze. "I was holding my own fine, got distracted. It happens." He ripped away the torn edge of his shirt with one hand, pinning the roll of gauze between his teeth. "Besides," he grunted, tearing off a good length of gauze and smoothing it over the wound, "That's no excuse."

Fai's eye watched with mild interest as an adhesive strip was taped over the bandaging with blood-smeared fingers.

"It doesn't matter," the blond cut in, his gaze darting away, "We won."

Kurogane stared at him incredulously a moment before huffing out a breath, throwing the rest of the gauze roughly back into the drawer.

"It _does _matter," he barked, "Maybe not for you, but it sure as hell does for me. You need to talk to me."

Muffled whispers melted into the room with the opening of the infirmary door, and the youngest of their group stepped in slowly, guided by a bouncing bundle of white and the hesitant touch of the boy beside her.

"Kurogane-san," Sakura said breathlessly, "I - I saw you fall, and...I came as soon as I could...are you alright?"

"M'fine," the warrior muttered, glancing up as Fai moved swiftly to support the young girl.

"Sakura-chan, you need to rest," he murmured, "Your leg..."

"I'm alright," she said quickly, shying away at the sight of dried blood on the blond's hands. Fai stilled, his lips parting, before he pulled them into a reassuring smile.

"Oh, of course. Syaoran-kun, why don't you help her back to the room?" The slight tremor in his voice faded with a quick swallow. "I'll go get us dinner, okay?"

"Mage," Kurogane called warningly, but Fai had already taken his greatcoat from Syaoran's outstretched arm and vanished behind the swing of metal doors.

* * *

The streets of Infinity's slate-gray downtown were shadowed by dim lighting and cool with the air of early winter. Fai pulled the lapels of his dark coat closer, fighting off the chill of the damp wind as he clutched the plastic bags of groceries he had picked up from the market a few blocks down.

He kept his gaze low, his shoulders hunched as he strode up the fogged sidewalk. He had been gone far longer than he should have - locked away in the dingy bathroom of the closest shop he could find, scrubbing his hands endlessly until his skin was raw and his fingers wrinkled, but he could still feel the heavy weight of another's blood on his hands, still _smell _it - and he knew he needed to head back now to avoid further suspicion.

The faint flicker of distrust in hazel eyes, mixed with the rough glare of a crimson gaze, had been enough to put an unwanted weight into his steps - but to see the same feelings reciprocated in emerald ones, as well, had torn him apart. The princess had always trusted him, always, through every lie and false grin; but today, he saw none of that. He saw fear.

He didn't realize that his foot had caught against an uneven patch of pavement until his shoulder made contact with the building beside him, harsh and abrupt. His breath hitched, a pained sound slipping from behind his teeth, and he leaned somewhat into the cold embrace of the concrete before the strain pulling on his legs became unbearable and he finally gave in.

He slid lopsidedly to the ground, the bags of groceries falling from his fingers. A weary sigh passing from him, he pressed his back against the wall and tilted up his head, his breath billowing into a white cloud that was carried away by the changing wind.

How had he suddenly become so weak?

Exhausted, he let his head fall, resting his forehead against his palm as a wave of nausea overtook him, and the bags beside him rustled angrily in the cool breeze, forgotten.

* * *

He returned later than expected, but the eyes that followed him did not press.

In near silence, his greatcoat still on and his movements sluggish, he cooked frozen slabs of chicken and tossed them into a bowl of flat noodles seasoned with butter and herbs. Fresh rolls were served alongside them, warm and flaky, just as he always used to love; but as he plated the food and set it on their small, age-worn table, he couldn't muster an appetite.

His stomach was prickling with hunger, but he knew that nothing on the plate he had set out for himself would suffice. He forced down a few bites of his roll, ate a few forkfuls of noodles, and chewed slowly - _savoringly_ \- on a few bites of chicken before pushing his plate aside.

Syaoran glanced at the ignored food, but said nothing. Mokona, though, perched on the boy's shoulder, tapped her small paws together and piped, "Why is Fai not eating?"

Kurogane clenched his jaw.

"I'm not that hungry tonight, Moko-chan," Fai said quietly, but the little creature spoke louder.

"But Fai hasn't been eating much all week!"

Kurogane stared at his plate, frowning a little before he leaned back in his chair and sighed.

"Let him be," he rumbled.

Mokona turned to face the warrior with a pout.

"Kuro-puu..."

"Just let him be."

He stood with a grunt and gathered both his empty plate and Fai's barely touched one, scraping off the contents of it and washing them out in the sink. Fai stared at him a little wordlessly a moment, then pressed his lips and stood also.

"Well, I think I'll get ready for bed. Goodnight, Moko-chan," he whispered, rubbing the furry head of the white creature gently, and then nodded to the two younger ones at the table. "Syaoran-kun, Sakura-chan." He hesitated, glancing back at the warrior behind him. "Kurogane."

The ninja didn't say a word, only listening to the slow footsteps of the mage's strides and the soft click of his bedroom door being drawn shut.

* * *

The first time Kurogane tried to get him to feed was unpleasant, at the least.

He strode into Fai's room with narrowed eyes, his tone low and growling as he swung the bedroom door shut behind him and stood in front of it, folding his arms.

"You're weak," he started, "You haven't had anything since Tokyo."

Fai, sitting on his bed with his lanky legs danging across the edge and his arms curled in his lap, didn't say anything.

"Mage," Kurogane barked, his brows furrowed, "You're starving yourself. You keep can't fighting matches like this."

"You think so?" Fai muttered, his lips twitching at a smile.

The ninja's face became blank aside from a deep crease in his brow, before he crossed the room to the front of the blond's bed, releasing a strained breath as one hand fell to the bandaging at his side.

Fai stared at him wide-eyed, his gaze darting from his chest to his face questioningly.

"What are you...?"

In a quick motion, Kurogane teared off the adhesive with a slight grimace, stripping away gauze and areas of healing skin to open the wound once more.

The scent of blood was overwhelming, filling Fai's lungs in a hot surge that took his breath away and wiped all traces of his thoughts clean except for _Prey_.

_Needpreyhungrybloodhotredneeditneedit_

_Mine._

Fai's breath had shuddered slightly, and he could feel the familiar glassing-over sensation of the vampire inside him worming it's way into every corner of his body, taking control.

A single gold eye had stared up at Kurogane's face, slitted and idle.

"Listen," Kurogane started, swallowing a little at the _heat_ in Fai's gaze, narrowed and demanding and predatory, "You need to tell me when you're hungry. I can't help you if I don't know."

Fai tilted his head somewhat, his gaze flickering down to rest on the opened wound. At the shift in attention, Kurogane's hand slid down to his side, smearing his fingers through the blood that had gathered sluggishly into the creases of half-healed skin, and held out his hand.

His pupils thinning, Fai regarded him almost distrustfully, his lips parting.

"You really shouldn't," he murmured, but it wasn't _Fai_ that said this, it was the _vampire_, voice velvety and thick with need.

Kurogane clenched his jaw, demanding quickly, "Take it."

Fai's pupils flared, his breath stilling in his chest a moment before something _consumed_ him, latching onto his nerves and making his throat dry, his mind foggy, and he had no control.

The blood on Kurogane's hand was hot, sliding down his tongue like melted chocolate, only so much better. It overwhelmed anything he had ever tasted. It was _alive_ \- pulsing and sparking with each swallow, staining his teeth, smoothing over his throat, and he _couldn't stop_.

But then it was gone. His eye slid open quickly, confused, before he looked at Kurogane's palm. He was still a moment, then hunger overtook him, and with shaking fingers he turned Kurogane's hand this way and that, searching for a drop of forgotten blood, he needed more, he wanted more, where was it, _no_ -

His gaze stuttered over to rest on the wound, still bleeding sluggishly, and his mouth went dry all over again.

He would have almost pounced, had it not been for the hand that clenched onto his shoulder.

"No," he panted, his hands pushing strongly against the arm that held him down, "_No_, more, I need -"

"_Mage_."

Startled, the vampire inside him shrunk away, and Fai blinked up at the fiery eyes that stared down at him. Then his gaze followed the curve of the warrior's arm, the scratches that littered it, and the vengefully-tight grip his own clawed fingers had on his forearm.

Instantly, his claws retracted, and his hands fell limp into his lap. It was only after a few more moments that Kurogane released his grip on his shoulder

"I..." Fai breathed out, but Kurogane shook his head at him, clearing his throat.

"Don't," he said quietly, "You okay?"

Fai blinked a few times, his breath coming shallow and slow, but the roaring, aching need in his stomach had finally subsided, if by a little.

"Yeah," he whispered. He swallowed somewhat, glancing away and speaking softly, "You should...you should clean that up."

Kurogane's hand fell to his side again, his jaw tensing. He only nodded, still a moment more before releasing a tense breath and walking out of the room. Fai watched the warrior's shadow stretch out against the sickly yellow hue of the hallway light before it disappeared.

* * *

"Fai-san?"

He blinked out of his daze slowly, his brow furrowing. They were alone again, the princess and him, shut away in the dim-lit space of her bedroom, their small sanctuary they had built for each other where pestering eyes couldn't follow them and they could just talk.

"Sorry," he stuttered, gathering his bearings and noticing the expectant tilt of Sakura's head, her hands reaching for the clasp of her frilled overcoat at the base of her neck. His fingers moved to undo it for her, and he slid the heavy fabric from her shoulders, setting it against the back of her bedside chair.

Sakura looked at him quietly, her thin lips pressed, before she crossed the small distance to her bed and sat down. She picked at her fingers, staring down at her lap quietly and sighing a little.

"Is everything alright?" she whispered, her pale brow puckered. "I mean, between us...we can still trust each other, right?"

The unsaid question was clear enough, in those words.

_Can I still trust you?_

"Of course, mi princia," Fai murmured gently, sitting beside her and taking one of her hands reassuringly in his. In the back of his mind, though, he knew this wasn't true. This was nowhere near true. He was unpredictable now, and he didn't know what to expect from himself anymore.

Sakura turned to look at him, her emerald eyes apprehensive. She released a slow breath, glancing at their hands.

"I'm sorry for how I acted yesterday," she murmured, "I...I know things are hard for you. I was being insensitive."

She had every right to be afraid. She had every right to know that she _should_ be. Fai swallowed quietly.

"No, it's alright," he replied, squeezing her hand gently, "You don't have to apologize."

Sakura hesitantly looked back up at him. She frowned somewhat before accepting his stance, and with a hand slowly raising to brush against his cheek, she shifted the subject.

"What does it feel like?" she asked quietly, her fingertips ghosting over the black cloth covering the hole that used to be his left eye.

Fai stared forward a moment, his jaw clenching. He looked down, clearing his throat.

"Like...someone else is in my body," he said hoarsely, "And I can't decide what I do anymore. They pick it for me."

"But, it's...it's still you, Fai-san," Sakura began, and Fai chuckled bitterly, shaking his head.

"No it's not."

Sakura's hand fell back to his cheek, her voice growing with determination.

"But it _is_. It's just another part of you, that's all." Her thumb rubbed across his cool skin tenderly. "You'll find a way to figure it all out and it will be okay. It will, Fai-san."

He fell silent at this, holding her hand unsurely and his brow wrinkling.

"And," the princess continued, her voice quieting, "Maybe if...if you're not ready to go to Kurogane-san...you can go to other people."

A shift rose in his consciousness, and he could feel the warmth of her thumb, the steady pulse beneath it, and gradually his eye drifted to rest on the vein that throbbed slowly in her thin neck.

He ripped his gaze away, his breathing shallow.

"No," he said suddenly, "Don't offer that to me."

"But Fai-san," Sakura protested.

"_Don't_."

Fai stared foward, his gaze cold, and he could feel the tension that sprung into the young girl's spine.

"Don't," he breathed, more gently, and slowly closed his eye. "Even you're trying to help me, that would still... It's not the same. It would make it worse." He cleared his throat, frowning. "Only Kurogane."

Sakura stared at him wordlessly a moment before nodding. The uneasy tightness in her bones loosened, and she held on to the blond's fingers a little tighter.

* * *

The process of feeding came slowly.

It took first steps from both of them. It was a while - despairingly long, hatefully dragged out - before Fai finally made the move to come to Kurogane, first. Through that, they worked through the steps together, if begrudgingly.

Offering preexisting wounds only tampered with the issue; Fai hadn't reached a point yet where only small tastes were desired, and so reopening old wounds resulted in limitation - the blood was in short and slow supply, and that only fueled a fire when Fai was hungry, as Kurogane had painfully found out.

The decision was made then that it had to be from fresh wounds. It needed to be an offering, a physical sort of ritual that displayed the role of predator and prey. Kurogane had made the decision to use his arm - it seemed the most logical place, easily accessible and not overly intimate. Biting into flesh, Fai had argued, was too personal, too close.

It had become routine, after that: make a small slice on his forearm, shallow enough to heal easily but deep enough to give Fai what he needed, let the creature that used to be the mage take control, and let the silent, painfully long moment - a single golden eye boring into dark red, glassed over and hazy and piercing all at the same time, nails pressing warningly against tanned skin and the heat of the blond's mouth casting shivers down his spine - pass until completion.

It wasn't exactly what was desired, but it was progress, and that was good enough.

* * *

The fogged morning sky filtered through the curtains with the musk of city smog and the promise of rain. Fai blinked slowly awake, breathed in the taste of moisture in the air, and grimaced.

The soft knock of Syaoran's scabbed knuckles rapped on his bedroom door.

"Fai-san, we have a match today," he said quietly. "You should get up."

The boy didn't linger, but Fai couldn't help the twinge that formed in his stomach, expecting a larger shadow to stand in the doorway, expecting to feel a heated gaze on his back, searching, waiting. But the warrior was not there, and soon Syaoran was gone.

He cleared his throat and sat up, rubbing his eye with a tired exhale, and squinted into the filtered gray light of dawn.

_It's just another day,_ he told himself softly.

* * *

**A/N - **I have wanted to do a little Infinity oneshot for as long as I can remember, but I could never really get ideas set in stone. I wanted to do one for a long time focusing on Fai and Sakura's relationship, but everything I tried writing was too short (it sneaked up in here anyway, no surprise there). And then I was just thinking of things relating to Fai's transformation and the adjustment that had to be made between/during the time from Tokyo to Infinity and I was like MY GOD THERE IT IS and I wrote this so fast like wow it is done. There is so much angst in this though (which should be expected tbh) but damn it drips with angst and angry vampire feels and I tried to portray the vampire side of Fai as very uncontrolled and animalistic and show how difficult that would be to sort of adapt to, so I think that came out well. ANYWAYS. (takes a breath)

Thank you so much for taking the time to read, and go ahead and drop me a review, I'd love to hear your ideas/suggestions! I know I need to work on BIA too (which I'm trying not to make crazy long but the chapters are long and UGH you feel me?) so I'm brainstorming on that, but I really just wanted to get writing on something, so I think I'm going to try to post some little oneshots pretty regularly just to get my thoughts flowing. Let me know what you think, and if you want to send me prompts I would love to read through some! Thanks again!


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